Synthetic model heme compounds will be prepared and their NMR and UV-visible spectra and kinetics of reaction with CO, O2 and isonitriles compared with those of oxygen-transporting hemoproteins such as hemoglobin and myoglobin. Heme cyclophanes having distal side steric effects and diheme compounds having linked CO binding will be studied in order to clarify the structure-reactivity relationships observed in hemoglobin and myoglobin. The kinetics and equilibria of O2, CO and isonitriles reacting with heme cyclophanes with varying steric hindrance will allow the proposals of preferential distal side steric effects to be tested.